1. Field of the Invention
The invention generally relates to a digital audio or video player or recorder and, more specifically, to a method of and a system for protecting the copyright of a program recorded on a storage medium such as a video tape, an optical disc, semiconductor memory, etc. in such a player or a recorder.
2. Description of the Prior Art
A variety of copy protecting schemes for various recording media have been proposed so far. In Digital Audio Tape (DAT) recorders for example, the Serial Copy Management System is used in which copy operation is controlled such that an original DAT tape is permitted to be copied only once.
As one of such copy protecting schemes, there is also known the Copy Generation Management System (CGMS) that uses two-bit copy generation management signals or flags. In this system, if the value of the two-bit signals recorded on a recording medium is xe2x80x9c00xe2x80x9d, then the copying of the recording medium is permitted unlimitedly; if xe2x80x9c10xe2x80x9d, then the copying is permitted only once; and if xe2x80x9c11xe2x80x9d, then the copying is prohibited. In the above-mentioned case of xe2x80x9c10xe2x80x9d in the two-bit signals, the copying involves a change of the value of the two-bit signals from xe2x80x9c10xe2x80x9d to xe2x80x9c11xe2x80x9d.
In one copy protection scheme used in video recorders that stores, on a recording medium, a transport stream (TS) based on the MPEG-2 (Moving Picture Experts Group phase 2) standard, a digital water mark is embedded in the transport stream in recording operation. The water mark is detected in playing operation to determine whether the recording medium should be played.
However, if a recorded recording medium is copied by using a player and a recorder, then any of the above mentioned authentication signals, i.e., the Serial Copy Management signal, the two-bit copy generation management signals and the digital water mark will be transferred from the player to the recorder. This gives an attacker a chance to counterfeit such the transferred authentication signal(s) such that the counterfeited authentication signal(s) has a value indicative of permission to copy the recording medium, permitting the attacker to make copies of the recording medium.
One solution to this problem was given by U.S. Pat. No. 5,659,613, which discloses xe2x80x9cMethod and apparatus for copy protection for various recording media using a video finger printxe2x80x9d. The method and apparatus use a combination of a Video Finger Print Signal and an Authenticating Signature to permit the player to handle either copy-protected or non-copy-protected media, in a manner that is difficult to compromise. The patent is hereby incorporated by reference.
However, it is preferable for the recording media player and/or recorder to have a higher copy protection capability. Though the higher the better, if the system becomes the more complicated, it won""t be desirable. It is also preferable for the recording media player and/or recorder to have a high degree of flexibility in dealing with recording media of various copy conditions such as a freely copy-able type, a one-generation copyable type (or a type having a one-time copy permission and having not been copied), a play-only type, and a pirated and even-play-prohibited type.
It is therefore an object of the invention to provide a recording media player and a recording media recorder provided with a high-security copy protection system of less complexity.
It is another object of the invention to provide a recording media player and a recording media recorder provided with a copy protection system stubborn to attacks and highly flexible in dealing with recording media of various copy conditions.
The above problems are overcome by a method of and an apparatus for recording a digital data stream on a recording medium in a recording format. The data stream includes a first protection level value indicative of a protection level of the program. The recording format comprises the cycle of a user area for containing data to be recorded and a system area for containing data necessary for the format. The system area includes an area whose data can not be rewritten by a second user (hereinafter, referred to as xe2x80x9cuser-unrewritable areaxe2x80x9d). The method and apparatus comprise the steps of and means for (a) recording the data stream on the recording medium by filling one user area after another, the data stream including a program of contents data, (b) recording a second protection level value indicative of the protection level assigned to the program in a first field of the user-unrewritable area, (c) recording a flag indicative of whether a source of the data stream is original or not in the first field, (d) generating a first value arbitrarily, (e) recording the first value in a second field of the user-unrewritable area, and (f) recording a second value given as a function of the first value in a third field of the user-unrewritable area.
According to an aspect of the invention, a prerecorded recording medium having a recording format comprising a cycle of a user area for containing data to be recorded and a system area for containing data necessary for the format is provided. The system area includes a user-unrewritable area whose data can not be rewritten by a user. The recording medium stores a sequence of digital data recorded in the user areas on the recording medium. The digital data sequence includes a program of content data in a predetermined format. A first protection level value indicative of a protection level of the program is embedded in the digital data sequence. A second protection level value indicative of the protection level assigned to the program is recorded in a first field of the user-unrewritable area. A flag indicating that the recording medium is original is also recorded in the first field. An arbitrarily generated first value is recorded in a second field of the user-unrewritable area. A second value given as a function of the first value is recorded in a third field of the user-unrewritable area.
According to another aspect of the invention, a method of and an apparatus including playing means for playing a recording medium already storing a sequence of digital data are provided. The sequence of digital data includes a program of compressed contents data in which a first protection level value indicative of a protection level of the program is embedded. The recording medium further stores, in at least one user-unrewritable area, a second protection level value indicative of the protection level assigned to the program, a flag indicative of whether the recording medium is original, an arbitrarily generated first value and a second value given as a function of the first value. The method or the playing means comprises the steps of or a plurality of means for (a) extracting the compressed contents data in the digital data sequence; (b) selecting one of predetermined modes of operation according to a combination of the second protection level value and the flag; (c) changing the selected mode to a play-prohibited mode if the selected mode is a copy permitting mode and if the recording medium is determined to be pirated from the first protection level value; (d) changing the selected mode to the play-prohibited mode if the selected mode is a presentation mode in which only expanded contents data is output and if the function is not true to the first and second values; (e) expanding and decoding the contents data into an expanded decoded contents data; (f) converting the expanded decoded contents data into an analog contents data; (g) terminating the steps or means (a), (e) and (f) in case of the play-prohibited mode; (h) outputting the analog contents data in case of the a presentation mode; and (i) outputting the analog contents data and the compressed contents data in case of the copy permitting mode.
The data stream may be encrypted with a key assigned for the program into an encrypted data stream, which is recorded on the recording medium. In this case, the key is encrypted with a master key into an encrypted key for use as the first value, which is recorded in the second field of said user-unrewritable area. The second value given as the function of the encrypted key is recorded in the third field of the user-unrewritable area. In playback operation, the master key-encrypted key is used as the arbitrarily generated first value. The second value is a value given as the function of the master key-encrypted key. The master key-encrypted key is decrypted with a stored master key into a decrypted value. The sequence of key-encrypted digital data is decrypted with said decrypted value into the digital data sequence.
According to further aspect of the invention, a method of and an apparatus for recording an analog data stream on a recording medium in a recording format are provided. The recording format comprises a first cycle of a user area for containing data of the data stream and a system area for containing data necessary for the format. The system area includes a user-unrewritable area whose data can not be rewritten by a first user, the method and the apparatus comprise the steps of and means for: converting the analog data stream into a compressed digital data stream having a data format comprising a second cycle of a program data portion and a user data portion in which a second user is permitted to include user data, the entire program data portions in the data stream constituting a program of content data; generating a first value at random, the first value being other than zero; generating a sample value from the program data portion; calculating a second value by using a function of the first value, the sample value and a predetermined value; inserting a sync data indicative of an existence of the second value and the sample value, the second value and the sample value in the user data portion of the compressed digital data stream; recording the first value in the user-unrewritable area included in the system area; and recording the compressed digital data stream on the recording medium by filling one user area after another.
The just-described method or apparatus produces an inventive prerecorded recording medium having a recording format comprising a first cycle of a user area for containing data to be recorded and a system area for containing data necessary for the format. The system area includes a user-unrewritable area whose data can not be rewritten by a user. On the recording medium there is recorded a sequence of digital data recorded in the user areas on the recording medium, the digital data sequence including a program of content data in a predetermined format, the predetermined format comprising a second cycle of a program data portion and a user data portion in which a user is permitted to include user data. The recording medium further stores an arbitrarily generated first value in the user-unrewritable area; a sample value generated from the program data portion, the sample value being inserted in the user data portion; a second value calculated by using a function of the first value, the sample value and a predetermined value, the second value being inserted in the user data portion; and a sync data indicative of an existence of the second value and the sample value, the sync data being positioned before the sample value and the second value in the user data portion.
The just-described prerecorded recording medium can be played by an inventive method of or apparatus including playing means for playing a recording medium already storing a sequence of digital data including a program of compressed content data having a predetermined data format. The recording medium stores an arbitrarily generated first value in a user-unrewritable area. The recording medium further stores, in a predetermined area of the predetermined data format, a sample value generated from the program data portion, a second value calculated by using a function of the first value, the sample value and a predetermined value. The method or the apparatus including the playing means comprise the steps of or a plurality of means for: (a) extracting the compressed content data in the digital data sequence; (b) making a test to see if the function is true to the first value, the second value, the sample value and a stored value which equals the predetermined value; (c) outputting a decoded version of the compressed content data only if the test has passed.
According to still another aspect of the invention, a method of and an apparatus for decoding an input data stream having a digital interface format according to the IEEE1394 standard into an analog video signal is provided. The input data stream includes a first code indicative of a protection level of a source of the input data stream. The method or the apparatus comprises the steps of or a plurality of means for: converting the an input data stream into an expanded decoded digital data stream in which a second code indicative of a protection level of a source of the input data stream is embedded; extracting the first and second codes; making a test based the first and second codes to see if the source is valid; and outputting an analog version of the expanded decoded digital data stream as the analog video signal only if it is determined in the test that the source is valid.